1. Field of the Invention
The invention relates to a turbojet engine for aircraft. More specifically, the invention relates to a regulation device used to regulate a flow-rate of cooling air in a thermal exchanger situated above the turbojet engine.
2. Background of the Invention
There are known ways of supplying an air-conditioning circuit in an aircraft pressurized cabin with a stream of compressed hot air tapped at the compressor of a turbojet engine. This stream of hot air is at least partially cooled by means of a cooling air stream tapped from the fan channel of the turbojet engine before it is injected into the air-conditioning circuit. The thermal exchange between the stream of hot air to be cooled and the stream of cooling air takes place in a thermal exchanger. The thermal exchanger comprises a case, generally rectangular, in which the stream of hot air and stream of cooling air circulate and cross each other.
In flight, the turbojet engines of an aircraft may work at different rates, depending on the needs of said aircraft, the rotational speed of the turbojet engines depending on the power requirements of the aircraft. For example, for takeoff, the aircraft needs maximum power and the turbojet engine then rotates at maximum speed. Conversely, during the descent and cruising stages of the aircraft, it is not necessary to have high power for the turbojet engines. This means that the rotational speed of said turbojet engines can be low. The compression and the air temperature in a turbojet engine depend on the power of said turbojet engine. Thus, the hot air tapped from the turbojet engine for injection into the air-conditioning circuit must be cooled to an extent that depends on its initial temperature.
In order to modulate the cooling of the hot air intended for the air-conditioning circuit, there are known ways of playing on the flow-rate of the cooling air stream in the thermal exchanger. For this purpose, a regulation device is used. This regulation device is directly positioned in a cooling air lead-in conduit that brings cooling air from the turbojet engine to the thermal exchanger. Generally, the cooling air lead-in conduit is formed by a circular-sectioned tube. The regulation device has a circular plate whose external contour substantially follows an internal contour of the cooling air lead-in conduit, and a rod around which the circular plate can rotate. The rod diametrically crosses the circular plate and is fixed by its two ends to the wall of the cooling air lead-in conduit. In the shutting position, the circular plate is positioned so that it faces the cooling air lead-in conduit, the axis of the circular plate being superimposed on the axis of said conduit, said circular plate completely shutting the conduit. In the open position, the circular plate of the regulation device is positioned in profile in the cooling air lead-in conduit so that the cooling air stream can pass from one side to the other of the circular plate and flow along the cooling air lead-in conduit. A quarter-turn rotation of the circular plate about the rod opens or closes the regulation device as needed. An electromechanical control system is used for the remote control of the regulation device so as to modulate the cooling air stream within the cooling air lead-in conduit so that the quantity of cooling air within the thermal exchanger corresponds to the quantity of cooling air needed to lower the temperature of the hot air stream to the desired temperature.
One drawback of a prior art regulation device such as this is that it generates hissing sounds which may be significant. Indeed, a front portion of the cooling air lead-in conduit is situated between the cooling air tapping zone and the circular plate. When the regulation device is closed, i.e. when the circular plate prohibits the passage of the cooling air stream, this front portion of the cooling air lead-in conduit forms a dead zone due to a stream of cooling air being sucked into said front portion.
It is an aim of the invention to provide a device capable of modulating the flow of a cold air stream, as needed, in an air passage channel designed to convey the flow of cold air into a thermal exchanger. It is another aim of the invention to provide a device of this kind that is of an easy design. It is an additional aim of the invention to provide a device of this kind that does not have the drawbacks of the prior art devices, and especially does not create a dead zone liable to emit hissing noises.
To this end, the invention proposes the making of a modulation device to modulate the stream of cold air in a thermal exchanger that is positioned no longer in the air passage channel supplying the thermal exchanger with cold air but upstream to this air passage channel, at the level of the cold air tap, i.e. directly at the level of the flow of air into the turbojet engine. Thus, when the modulation device is open, a stream of cold air gets sucked into the cold-air passage channel. When the modulation device is closed, all the cold air flows along the turbojet engine, in sliding along the modulation device but without being even partially deflected. No stream of cold air can penetrate the air passage channel when the modulation device is closed.
Advantageously, the cold air stream modulation device is made in a pre-existing part of the turbojet engine. The modulation device is, for example, made on a fixed vane located at the exit of the fan of the turbojet engine. Indeed, a turbojet engine is provided with a plurality of fixed vanes, located downstream with respect of the fan and designed to bring the whirling air stream coming out of said fan into the axis of the turbojet engine. The fixed vanes are static, rectilinear parts in the turbojet engine whose function in the prior is the purely aerodynamic one of imposing a direction on the air stream in the turbojet engine. The invention uses at least one of these fixed vanes, situated so as to be facing the flow of the air stream from the turbojet engine, to form the inlet of the cold air passage channel designed to supply the thermal exchanger. The air stream coming from the fan, and designed to flow into the turbojet engine, first flows along the fixed vanes. Thus, a portion of this air stream may be diverted and made to go through an internal volume of the vane in order to be brought into the thermal exchanger.
The regulation device comprises, for example, an aperture shut by a door whose travel may vary according to needed. This aperture lets a portion of the air stream through into the air passage channel. This deflected air stream is then conveyed to the thermal exchanger. Should the modulation device be made on a fixed vane, the structure of said vane is modified so as to present an internal volume. It is then enough to make an aperture on one of the flanks of this hollow structural section so that, once the aperture is made, the cold air stream can rush into it. The vane thus forms the inlet to the air passage channel, the internal volume of said vane forming a front part of said channel. The air passage channel continues up to the thermal exchanger into which it leads.